1. Field of the Disclosure
The present disclosure relates generally to fusing toner to sheets of media, and particularly to a heater and heating method for the fuser assembly of a printing device that provides for better heating control while reducing flicker and harmonic noise.
2. Description of the Related Art
As printer speeds increase, fusing power to fuse toner to sheets of media increase. Existing 1200 W fuser heaters used in color electrophotographic imaging devices are not able to deliver enough power for maintaining the needed fusing temperatures at 70 pages per minute (ppm). To fuse 70 ppm in a color imaging device, heater power would need to increase to roughly 1450 W or higher in order to robustly maintain fusing temperatures and achieve required fusing quality for all possible operating conditions.
An issue for a fuser heater with power higher than 1200 W is meeting flicker and harmonics requirements of the International Electrotechnical Commission (IEC). When a high power fuser heater is turned on, light bulbs flicker in the room in which the imaging device is located if the light fixtures are on the same branch circuit as the imaging device. To reduce the severity of light flicker and achieve relatively tight temperature control requirements due to a relatively small fusing temperature window, phase control of AC power is used to adjust heating power by changing the phase angle or phase time delay for each AC half cycle. For fuser heaters having a single resistor trace for generating heat, flicker and harmonics generated by the fuser heater during a fusing operation is directly related to fuser heater power. Higher power levels will thus worsen flicker and harmonics effects. Fuser heater power levels at about 1200 W in current imaging devices are very close to the power limit that can pass flicker and harmonics tests at 70 ppm print speeds. Even for a 1200 W fuser heater, considerations exist to sacrifice temperature control performance and allow fuser heater temperatures to vary significantly around its heater set point in order to pass flicker and harmonics requirements. Because fusers for color laser printers typically have very small operating windows, it is very challenge for a 1200 W fuser heater to achieve tight temperature windows while passing flicker/harmonics tests. Fuser assemblies having 1300 W or 1450 W fuser heaters further increase the challenges.